/Engine/Plugins/Developer/Concert/ConcertMain/Source/ConcertServer/Public/IConcertServer.h
Callback to check whether a participant should be allowed to join a session.
[FOnConcertParticipantCanJoinSession](API\Plugins\ConcertServer\FOnConcertParticipantCanJoinSess-) & OnConcertParticipantCanJoinSession()